The present invention relates to a method for the selective degradation of milk proteins, and in particular to a method for the selective hydrolysis of casein and/or casein/caseinate in the presence of at least one further protein constituent other than casein/caseinate.
The invention more in particular relates to such a method wherein the further protein constituent is a milk protein (constituent) other than casein, in particular a whey protein (constituent), and/or to such a method wherein the casein/caseinate and preferably also the at least one further protein constituent are essentially in solution, in particular essentially in an aqueous solution.
According to the method of the invention, the casein/caseinate is specifically degraded in the presence of the at least one further protein constituent, said further protein constituent essentially remaining intact in the process. This allows the casein hydrolysis fragments to be separated, in a further separation step, from the one or more further protein constituents which have essentially remained intact.
The invention is based on the surprising finding that certain proteinases exhibit a very high specificity with respect to casein in the presence of other proteins, in particular in the presence of other milk proteins such as whey proteins. The invention is further based on the use of these specific proteinases in the hydrolysis of casein-containing protein preparations, in particular casein preparations or (aqueous) solutions of milk proteins, such as milk.
The method of the invention can be used, in a first embodiment, for the preparation of a casein hydrolysate which has been stripped of one or more immunogenic protein components other than casein. In a second embodiment, the invention can be used for preparing a milk protein preparation, in particular a whey protein preparation which is essentially stripped of casein/caseinate, starting from a casein-containing milk protein preparation such as milk, whey or a solution of milk or whey proteins. These whey protein preparations stripped of casein likewise have beneficial properties from an immunological point of view.
The invention will be further discussed with reference to these specific, non-limiting embodiments xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d, which are schematically shown in FIG. 6. Both embodiments comprise the step of selectively degrading casein in the presence of at least one further proteinaceous component, and separating the hydrolysed fragments from the non-degraded proteins, but differ in the starting material used, the product desired, as well as the intended use and required (immunological) properties of said product, as will become clear hereinbelow.
EP-A-0 250 501 describes a method for producing a whey protein hydrolysate, comprising the steps of:
a) removing casein from the whey protein starting material;
b) hydrolysis of the casein-free protein material obtained in (a) with at least one protease;
c) ultrafiltration of the hydrolysate of (b) using a membrane with a xe2x80x9ccut-offxe2x80x9d value of no more than 20,000 Dalton;
and optionally further processing of the filtate thus obtained.
In step a), the casein is removed from the whey protein starting material by either physical separation such as precipitation or filtration; or enzymatically by the use of the neutral metalloprotease of Bacillus subtilis (Neutrase(copyright), Novo Industrie A/S), which is said to have xe2x80x9ca high activity against casein but no or only a weak activity against both native as well as heat-denatured whey proteinsxe2x80x9d.
The enzymatic hydrolysis is carried out at a pH of 4-9, preferably pH 7.5, and a temperature of 30-60xc2x0 C., preferably 50xc2x0 C., until xe2x80x9ccompletionxe2x80x9d, which is said to be a degree of hydrolysis (DH) of about 4%, based upon total protein. The casein fragments are then removed by means of centrifugation or ultrafiltration usingxe2x80x94when the whey protein starting material has not been heat-treatedxe2x80x94a membrane with a xe2x80x9ccut-offxe2x80x9d value of no more than 20,000.
Because the molecular weight of the different caseins (19.5-25 kDa) are in the same range as the molecular weights of the native whey proteins xcex1-lactalbumin (14.2 kDa) and xcex2-lactoglobulin (18.2 kDa (monomer)) it is doubtful whether the use of a 20 kDa membrane will lead to the separation of the hydrolysed caseins from the whey proteins.
The xe2x80x9ccasein-freexe2x80x9d whey proteins thus obtained are then further hydrolysed using enzymes such as Alkalase(copyright) 2.4 L and Rhozyme P41(copyright), and then ultrafiltrated. According to this disclosure, by selectively removing the casein before the whey proteins are hydrolysed, the final whey protein hydrolysate will have a less bitter taste.
However, the casein depleted whey protein preparation obtained after said step a) is only an intermediate product, and not the end product. Accordingly, no immunological determination of the allergenic properties of this intermediate product is given. In the method of EP-A-0 250 501, this is also not essential, as the proteins obtained are hydrolysed further, after which any still remaining antigenic fragments can be removed by ultrafiltration. However, from the low degree of hydrolysis (4%) in step a), it is expected that at least some antigenic casein fragments will be present in said intermediate product.
EP-A-0 384 303 describes a method for hydrolysing proteins, especially milk proteins and whey proteins, in which a combination of a proteinase preparation from Aspergillus sp. and a bacterial aminopeptidase is used. The use of this combination provides an end product with a less bitter taste, at a higher degree of hydrolysis: with said combination, the xe2x80x9cbitter pointxe2x80x9d is reached at a DH of 4.4%, whereas the bitter point is said to be reached at 1.2% when only the proteinase is used.
EP-A-0 610 411 discloses a method for obtaining a casein hydrolysate, in which a casein or caseinate is suspended in an aqueous medium and hydrolyzised to a DH of 15-35%, preferably 22-28%, using a combination of proteases from the following three groups:
1) one or more neutral endoproteases of a Bacillus (such as Neutrase(copyright));
2) one or more basic endoproteases of Bacillus (such as Alcalase(copyright), Esperase(copyright) and Savinase(copyright)) and
3) an endoprotease of Aspergillus (such as Novozym(copyright) 515).
According to this reference, the use of such a combination of proteases, and hydrolysis to a DH of 15-35% (compared to 4.4% such as disclosed in EP-A-0 250 501 as well as for instance EP-A-0 384 303) provides an improved casein hydrolysate. Nevertheless, no immunological determination of the antigenic properties of the hydrolysate thus obtained is disclosed. Also, the enzymes used are obtained from Bacillus subtilis, which is not a food grade microorganism.
EP-A-0 631 731 describes a method for producing a partial hydrolysate of milk protein by enzymatic hydrolysis of a mixture of whey protein and casein to a DH between 4 and 10%. Although a reduction in antigenicity of 80% or more was obtained, according to the examples the resulting hydrolysates still had some residual antigenicity as determined by an ELISA.
EP-A-0 421 309 describes a method for preparing a whey protein hydrolysate free of allergenics by pepsin prehydrolysis, followed by trypsin-chymotwpsin hydrolysis in the presence of a cathionic serine endoprotease of type elastase 2.
Derwent Abstracts AN-96-471202 and AN-94-337356 (corresponding to JP-08238059-A and JP-06261691-A) disclose a method for producing a low-allergenic milk protein preparation, in which alpha-casein is selectively decomposed using a fungus derived protease, in particular from the geni Mucor and Cladosporium.
Derwent Abstract AN-95-307065 (corresponding to JP027203844 A) discloses a method for preparing an emulsified whey protein hydrolysate with good thermo-stability and up to 0.0001 residual antigen in ELISA, obtained by hydrolysing a solution of milk whey protein with a mixture of endotype proteases from Bacillus subtilis, trypsin and papain.
EP-A-0 601 802 describes a method for removing allergenic compounds from proteinaceous compositions, in which the protein in said composition is decomposed with proteolytic enzymes into a protein hydrolysate having a degree of hydrolysis of 20-60%, followed by clarification of the hydrolysate thus obtained, preferably by centrifugation or ultrafiltration.
Macropeptides still remaining in the intermediate product thus obtained (which according to Table 2 still contains xcex2-lactoglobuline as shown on ELISA) are then removed using an absorption resin. As the proteolytic enzyme trypsin, pancreatin or microbial proteases such as Alkalase(copyright)0.6 L from Bacillus licheniformis can be used.
B. Kiefer-Partsch et al., Appl.Microbiol.Biotechnol. (1989) 31:75-78 describes the purification of an X-prolyl-dipeptidyl aminopeptidase from the cell wall proteolytic system of Lactococcus lactis sp. cremoris. This enzyme is described as a metal-independent, highly xcex2-casein specific protease; reference is made to similar enzymes from L. lactis en Streptococcus thermophillus. These enzymes are however not used for producing a casein hydrolysate, or specifically removing casein from a whey protein mixture.
A. Preparafion of a Casein Hydrolysate which Has Been Stripped of One or More Protein Constituents Other than Casein
This embodiment of the invention relates to the preparation of a casein hydrolysate which has been stripped of one or more immunogenic protein components other than casein.
This embodiment particularly relates to a method for preparing a casein hydrolysate free from ABBOS epitopes, and to the casein hydrolysate free from ABBOS epitopes thus obtained.
An ABBOS epitope is to be understood, hereinafter, as that part of the antigenic ABBOS peptide/fragment of bovine serum albumin (BSA) which reacts with an antibody directed to the ABBOS peptide.
A casein hydrolysate free from ABBOS epitopes is to be understood hereinafter as a casein/caseinate hydrolysate which does not contain any peptides or peptide fragments which may form a bond with antibodies to ABBOS epitope (cross-reaction).
It is known that proteins from cow""s milk may give rise, because of their antigenic properties, to immunological reactions, particularly in neonates/infants. These immunological reactions can manifest themselves, for example, as hypersensitivity reactions (cow""s milk protein allergy).
One of the immunological reactions against proteins from cow""s milk, which has received a great deal of attention in recent years, is the reaction against (epitopes of) bovine serum albumin (BSA) in infants, because of the role played by this immune response in the onset of type I Diabetes Mellitus.
There are indications that, in infants, immunoglobulin G (IgG) antibodies against a specific region of BSA (amino acids 126-144, the so-called ABBOS peptide) can be generated which, under certain conditions, are cross-reactive with the homologous structure in the P69 protein on the surface of pancreatic beta cells. This may give rise to an autoimmune reaction leading to the destruction of the beta cells and consequently to a failure in insulin production.
These findings are based, inter alia, on the fact that the ABBOS epitope is not completely broken down in the digestive tract, even though it contains a large number of possible attack/cleavage sites for the proteolytic enzymes in the gastrointestinal tract. Earlier studies have produced, inter alia, the following results:
in the blood of infants in which diabetes has been diagnosed, antibodies to BSA and in particular to the ABBOS peptide can be detected;
the physiological digestion of BSA proceeds less efficiently in infants than in adults, due to the higher pH in the stomach;
The result is that fragments of BSA containing the intact epitope of the ABBOS peptide are still present after digestion. As in infants, some parts of the mucosal barrier are not yet completely developed and/or harmonized, these large peptide fragments can pass through the intestinal wall and reach the blood stream. These foreign proteins would then stimulate the immune system of the infant to produce antibodies which may possibly be directed against the ABBOS epitope.
Other proteins in cow""s milk which may give rise to immunological reactions are, inter alia, xcex1-lactalbumin (xcex1-Lac), beta-lactoglobulin (xcex2-Lg), bovine immunoglobulin G (IgG) and the caseins, as well as antigenic fragments thereof.
In the prior art foods have therefore been developed, in particular for infant formulas, which are based on cow""s milk protein which has been degraded/hydrolysed by certain enzymes, resulting in a reduction in the antigenic properties of the milk proteins. Milk protein hydrolysates (xe2x80x9chypoallergenic hydrolysatesxe2x80x9d) for the preparation of such foods are likewise commercially available.
Such hydrolysates are obtained by the treatment of milk protein with proteolytic enzymes (proteinases), leading to the degradation of both the casein and/or the caseinate, whichxe2x80x94in terms of protein (determined as dry substance)xe2x80x94forms the main constituent ( greater than 80 wt %) of milk proteins, as well as all the other proteins present, including the antigenic proteins and their epitopes.
Studies by the applicant have shown, however, that the commercially available milk protein hydrolysates generally still give cross-reactions and/or exhibit antigenic properties, particularly in specific in vitro immunological assays such as enzyme-linked immunosorbent assay (ELISA). For example, these known hydrolysates still contain BSA fragments which exhibit cross-reactivity with the ABBOS peptide and/or contain intact ABBOS epitopes. Studies by the applicant have demonstrated the presence of these epitopes by means of immunological assay techniques using ABBOS-specific antibodies.
These cross-reactive fragments/immunogenic components could in theory be removed by a higher degree of hydrolysis of the milk protein hydrolysates. This, however, leads to an unduly high level of undesired xe2x80x9cfreexe2x80x9d amino acids in the final product, which are less well absorbed through the intestinal wall and, moreover, may detract from the properties of the product, in particular its consistency and osmolality. The known hydrolysis processes cannot be adequately controlled in this respect.
It is therefore a first object of the invention to provide a milk protein preparation, in particular a casein/caseinate hydrolysate, which has improved immunological properties.
It is a further object of the invention to provide such a preparation which has an acceptably low level of free amino acids.
In particular it is an object of the invention to provide a casein/caseinate hydrolysate in which essentially no antigenic components of the ABBOS peptide are still present/detectable.
Further objectives and advantages of the invention will become clear from the following description.
We have now found that certain proteinases from lactococci exhibit very high specificity to casein/caseinate, i.e. that they degrade the casein/caseinate in milk protein very selectively, whereas the other protein constituents present, with the antigenic epitopes, remain essentially intact.
This surprising finding makes it possible, after prior hydrolysis of the milk protein, for the (relatively) small casein hydrolysis products to be separated, in a simple manner, from the still virtually intact antigenic (whey) proteins, giving a casein hydrolysate which has essentially been stripped of one or more specific antigenic components such as antigenic whey proteins, and in particular of antigenic components of BSA such as the epitope of the ABBOS peptide.
The invention therefore relates, in a first aspect, to a method for preparing a hydrolysed milk protein preparation, starting from a milk protein preparation which comprises more than 80 wt %, preferably more than 90 wt %, of casein/caseinate and at least one further (milk) protein constituent, in which the milk protein preparation is brought into contact with a proteolytic enzyme under conditions for the hydrolysis of the casein/caseinate, characterized in that the casein/caseinate and preferably also the at least one protein constituent are in an essentially dissolved state, and in that the proteolytic enzyme is a proteinase specific for casein/caseinate, such that the casein/caseinate is hydrolysed while the at least one (milk) protein constituent remains essentially intact.
In a further aspect, the invention relates to a method for preparing a milk protein hydrolysate which has been stripped of at least one antigenic protein constituent, starting from a milk protein preparation which comprises more than 80 wt %, preferably more than 90 wt %, of casein/caseinate and the at least one antigenic protein constituent, comprising the steps of:
a. bringing the milk protein preparation into contact with a proteinase specific for casein/caseinate, the casein/caseinate and preferably also the at least one protein constituent being in an essentially dissolved state, such that the casein/caseinate is hydrolysed while the at least one antigenic protein constituent remains essentially intact,
b. separating the casein hydrolysis fragments and the at least one antigenic protein constituent which has remained essentially intact.
In particular, the invention relates to such a method for preparing a hydrolysed casein preparation which does not contain any (antigenic components of) BSA, in particular no (epitopes of the) ABBOS peptide.
The invention further relates to milk protein hydrolysates obtainable according to the method of the invention, in particular to such a hydrolysate which is xe2x80x9cfree from ABBOS epitopesxe2x80x9d.
In the description and the claims, protein contents are expressed on the basis of total protein, i.e. in per cent by weight based on the total protein content, in particular determined as dry substance, in the absence of a statement to the contrary.
According to the invention, the casein/caseinate is essentially in solution, preferably in aqueous solution. The at least one further protein constituent, and preferably (virtually) all further protein constituents present, are likewise preferably essentially in solution, more preferably in aqueous solution. The term xe2x80x9cessentially in solutionxe2x80x9d should be understood as customarily used in the dairy industry, i.e. that the constituents in question are virtually entirely dissolved or are virtually entirely in a dissolved state, for example as a suspension of micelles.
This means, incidentally, that there is an upper limit to the casein/caseinate concentrationxe2x80x94based on total solutionxe2x80x94of the starting material, depending on the solubility of casein in the medium used. In general, the casein concentration will be less than 20 wt % and in particular less than 15 wt %, based on the total composition.
A casein-specific proteinase is to be understood, in particular, as a proteinase which degrades casein selectively in the presence of one or more of the whey proteins xcex1-Lac, xcex2-Lg, BSA and IgG. The selectivity of such proteinases is preferably such that, given equal ratios of enzyme/substrate an within a given time period, the proteinase degrades more than 90% of the intact casein and less than 5% of each of the whey proteins mentioned.
It should be understood, however, that the invention does not exclude the possibility that the antigenic proteins to be removed are cleaved to a lesser extentxe2x80x94albeit much less rapidly than the casein/caseinatexe2x80x94to produce (large) protein fragments, as long as these antigenic protein fragments can be separated from the casein fragments obtained after hydrolysis, the separation taking place, in particular, on the basis of molecular size or molecular mass.
The proteinases (also referred to as proteases) used in the invention preferably are derived from lactococci, more preferably from xe2x80x9cfood gradexe2x80x9d lactococci, or possibly other suitable xe2x80x9cfood gradexe2x80x9d microorganisms. In lactococci the proteinases are present, in particular, on the outside of the cell wall.
Some nonlimiting examples of suitable proteinases, which may or may not be derived from food grade organisms, are the cell wall proteinase of Lactococcus lactis subsp. cremoris, strain Wg2, collagenase (particularly from Clostridium histolyticum) and Dispase, (particularly from Bacillus polymyxa) and the like, as well as the variants thereof obtained by recombinant-DNA techniques, if these have the desired substrate specificity.
An example of a commercially available enzyme suitable for use in the invention is Neutrase(copyright) (Novo Industri), although this may possibly provide a product with a somewhat more bitter taste and/or may possibly be less selective, compared to the enzymes mentioned above.
Those skilled in the art will be able, on the basis of the present disclosure and/or by means of simple tests for determining the specificity/activity with respect to casein and the further protein constituents of milk protein, to find other suitable proteolytic enzymes, which may be native or recombinant.
While a number of these proteinases and their use in cheesexe2x80x94making have been described in the prior art, their surprising substrate specificity with respect to casein has not previously been reported or utilized.
The proteinases can be used in any suitable form, including enzyme preparations or enzyme isolatesxe2x80x94which can be obtained in a manner known per se and/or are commercially availablexe2x80x94as well as in immobilized form. Mixtures of more than one proteinase can likewise be used, as long as the desired specificity with respect to casein/caseinate is retained.
Owing to their specificity, the proteinases will in particular cleave/hydrolyse the protein bonds in the casein; in the widest sense, however, the invention is not limited to a specific type of enzymatic reaction.
In a further aspect, the invention relates to the use of the above-described specific proteinases in the conversion of a milk protein preparation which comprises more than 80 wt %, preferably more than 90 wt %, of casein/caseinate and at least one further protein constituent, the casein/caseinate and preferably also the at least one protein constituent being in an essentially dissolved state, preferably in aqueous solution.
The milk protein preparations which are used in the invention, in particular casein preparations or casein-enriched milk or milk protein preparations, are commercially available and/or can be obtained in a manner known per se, starting from (cows"") milk or milk products. The invention is however not limited to milk or milk preparations derived from a specific animal. For instance, besides cows"" milk, milk from goat, sheep, or any other mammal, or mixtures thereof, can also be used as the starting product.
In addition to casein/caseinate ( greater than 80 wt %, preferably  greater than 90 wt %), these preparations generally contain further milk proteins such as BSA, xcex1-Lac, xcex2-Lg and IgG, in amounts of less than 20 wt %, in particular less than 10 wt %. However, it will be clear to those skilled in the art that, where appropriate, milk or other protein preparations having low(er) casein levels, for example containing as low as 40 wt % of casein, can also be used, although this may in some applications lead to a lower yield of casein hydrolysate, based on the starting preparation, and consequently a less efficient process.
For instance, the starting product can be a mixture of casein or a casein containing protein preparation, and non-milk proteins, such as soy protein or a soy protein preparation. It is known that soy protein can be used in foods, including infant formulas, to replace animal derived proteins or protein products, in order to reduce the allergenic properties of said food. In such foods, soy protein can also be combined with casein hydrolysates or other milk protein hydrolysates.
Such foods can also be prepared according to the invention, for instance by mixing a casein hydrolysate obtained according to the invention with the desired amount of soy protein and further constituents known per se.
Alternatively, such foods can be prepared by providing a mixture of casein or a casein containing preparation (such as milk or a milk protein preparation) and the soy protein, and selectively hydrolysing the casein in said mixture in situ using a selective proteinase as described herein. If required, any large intact proteins, such as those also described herein, can then be selectively removed. It will be clear to the skilled person that, in this latter embodiment of the invention, the casein concentration in the starting mixture will generally be less than 80%.
Therefore, in a further embodiment, the invention relates to a methodxe2x80x94as described hereinxe2x80x94for selectively hydrolysing casein in a mixture containing at least one non-milk protein or protein component, such as soy protein, to provide a protein preparation containing at least the non-milk protein and the hydrolysed casein fragments.
Another embodiment of the invention in which the casein concentration in the starting preparation can be less than 80% comprises the use of a starting material comprising a mixture of casein or a casein containing preparation, and milk protien or a milk protein preparation, for instance in an amount of 5-50 wt %, preferably 20-40 wt % of the mixture. Again, in such a mixture, the casein can be hydrolysed selectively in situ using the method described herein, after which optionally undesired peptides can be removed.
The hydrolysis of the milk protein preparation is performed in a manner known per se, under conditions suitable for the desired enzymatic conversion, such as a temperature of 20-40xc2x0 C., a time of 4-16 hours, and a pH of 6-8, and using known equipment and techniques. In the process, the use of the specific proteinases may additionally provide improved control of the enzymatic conversion.
The hydrolysis is carried out to a suitable extent, i.e. to a degree which allows the hydrolysed fragments to be separated from the nondegraded protein constituents, which is dependant upon factors such as the antigenic components to be removed, the separation method to be used (in particular the molecular cut-off value of the ultrafiltration membrane to be used), and further factors clear to those skilled in the art.
The degree of hydrolysis is preferably such that any subsequent ultrafiltration step can be carried out in a technically/industrially acceptable manner (with respect to filtration rate, yield and the like).
The hydrolysis is terminated before too high a level of xe2x80x9cfreexe2x80x9d amino acids is obtained. The level of free amino acids in the preparation obtained after hydrolysis will, as a rule, be less than 5 wt %.
The progress of the hydrolysis can be monitored, if required, by a suitable technique such as DH (degree of hydrolysis) assay by measuring, for example, the consumption of alkali, or with the aid of the OPA (=O-phthalic anhydride) method, alternatively with the aid of a chromatographic method such as RP-HPCL (reverse-phase high performance liquid chromatography) analysis.
After the hydrolysis, the hydrolysed casein fragments can be separated from the (virtually) intact, nondegraded other proteins or large protein fragments. Any suitable separation method can be used for this purpose, in particular a separation method on the basis of molecular mass and/or molecular size, especially ultrafiltration. This process can advantageously make use of ultrafiltration equipment generally known in the dairy industry, often already present within the dairy industry itself.
In ultrafiltration, use is made of a membrane having a suitable molecular cut-off value, preferably 30 kDa or less, more preferably 10 kDa or less, preferably less than 1 kDa, depending on the size of the antigenic proteins/protein components to be removed.
To obtain a preparation free from ABBOS epitopes, generally a membrane will be used having a molecular cut-off value of 30-10 kDa , IgG (molecular mass 146,000) being removed at the same time. To remove other proteins, in particular smaller immunogenic components such as xcex1-Lac and xcex2-LG, it is possible to use membranes having a molecular cut-off value up to 5 kDa or less.
As a rule, the immunological purity of the hydrolysate will increase the further the caseins are hydrolysed and/or the lower the molecular cut-off value of the membrane used. The ultrafiltration rate (the throughput through the membrane), and also the yield, will likewise depend on the combination of the degree of hydrolysis and the ultrafiltration membrane used.
The immunological purity of the hydrolysate can be assayed by means of a suitable immunological assay, in particular using one or more antibodies which are specific for the antigenic proteins or fragments thereof, and/or the epitopes in question. Suitable techniques such as ELISA and suitable specific antibodies will be known to those skilled in the art and/or can be obtained in a manner known per se.
According to the invention, a hydrolysate is regarded as free from an antigenic component if, using such an immunological assay and in particular ELISA, it is no longer possible to observe/detect any antigenic reaction.
Although the invention allows immunologically highly pure hydrolysates to be obtained, which are essentially free from a more than one, or all, of the immunogenic components present in milk protein, such as BSA/ABBOS, xcex1-Lac and xcex2-Lg and/or IgG, and are even free from immunogenic components/epitopes of the casein/caseinate itself, the method according to the invention is especially suitable and intended for preparing a hydrolysate which is xe2x80x9cBSA-freexe2x80x9d or xe2x80x9cfree from ABBOS epitopesxe2x80x9d.
In the preparation of such a xe2x80x9cBSA/ABBOS-freexe2x80x9d hydrolysate it is not required given that BSA is a relatively large proteinxe2x80x94to hydrolyse to as high a degree as required for the (simultaneous) removal of smaller antigenic proteins such as xcex1-Lac and/or xcex2-Lg. Also, ultrafiltration membranes having a higher molecular cut-off value can be used, as stated above. This has the advantage that the available equipment is less occupied (shorter reaction time for the hydrolysis, better throughput in the ultrafiltration), resulting in a higher production per unit time.
It is therefore not excluded that, in a hydrolysate xe2x80x9cfree from ABBOS epitopesxe2x80x9d according to the invention, (components/epitopes of) other antigenic proteins, in particular smaller one, such as xcex1-Lac and xcex2-Lg, may still be detectable. Likewise it is possible for the preparations of the invention still to contain antigenic components of the casein/caseinate itself.
The casein hydrolysates according to the invention can be further used and/or processed in a manner known per se, for example for the preparation of hypoallergenic foods such as infant formulas and enteral foods, which can be used for preventing and/or treating cow""s milk protein allergy, in particular Diabetes Mellitus type I caused by immunological reactions against BSA/ABBOS.
B. Preparing a Whey Protein Preparation Stripped of Casein/Caseinate
The second embodiment of the invention relates to the preparation of a milk protein preparation, in particular a whey protein preparation, which is essentially stripped of casein/caseinate, starting from a casein-containing milk protein preparation, in particular whey or a solution of whey proteins.
More in particular, this embodiment relates to a method for preparing a protein preparation having a reduced casein content and comprising at least one protein constituent other than casein/caseinate, starting from a protein preparation which comprises the at least one protein constituent and casein/caseinate, in which the starting preparation is brought into contact with a proteolytic enzyme under conditions for the hydrolysis of the casein/caseinate, characterized in that the casein/caseinate and preferably also the at least one protein constituent are in an essentially dissolved state, and in that a proteolytic enzyme is a proteinase specific for casein/caseinate, such that the casein/caseinate is hydrolysed while the at least one protein constituent remains essentially intact.
In this embodiment of the invention, a casein-specific proteinase as described above is likewise used, in particular for the specific degradation of the casein/caseinate in the presence of the at least one further protein constituent.
Other than in the above-described embodiment, however, subsequently the one or more further (milk) protein constituents which have essentially remained intact are obtained, instead of the casein hydrolysis fragments.
A casein epitope is to be understood herein as those parts of the casein molecules or casein fragments in the starting material which react with an antibody to casein.
A protein preparation free from casein epitopes is to be understood hereinafter as a protein preparation which does not contain any proteins or protein fragments which are able to form a bond with antibodies to a casein epitope (cross-reaction).
Such preparations stripped of casein, casein fragments and/or casein epitopes are important because of their reduced immunological characteristics. Thus, Cavallo et al., The Lancet, 1996; 348:926-928 report that xcex2-casein is possibly involved in insulin-dependant diabetes, since early consumption of cow""s milk may cause a specific immune response to xcex2-casein, which cellular and humoral anti-xcex2-casein immune response may produce a cross-reaction with proteins on the pancreatic beta cell, inter alia because of the high homology between the sequences of xcex2-casein and various beta cell molecules. In this respect, milk protein preparations stripped of casein may play an important part in the preparation of non-immunogenic infant formulas.
The present embodiment of the invention generally comprises the following steps:
a. bringing the protein preparation, which comprises the at least one desired protein constituent and casein/caseinate, into contact with a proteinase specific for casein/caseinate, such that the casein/caseinate is hydrolysed while the desired protein constituent remains essentially intact,
b. separating the casein hydrolysis fragments from the desired protein constituent which has essentially remained intact.
This embodiment of the invention can be used for the selective removal of casein/caseinate from casein-containing protein preparations, to provide a protein preparation stripped of casein, the selective removal of even low to very low casein levels being possible in the process.
This embodiment can be used, in particular, to remove casein from milk or a solution of milk proteins, and in particular from whey or a solution of whey proteins.
The casein level of the starting preparation will, as a rule, be at least 0.1 wt %, in particular 1 wt % or more, although even lower amounts of casein can also be selectively removed. The upper limit for the casein content is not essential, although in practice the casein content in the starting material may generally be less than 50% by weight, preferably less than 20% by weight, more preferably less than 10% by weight.
The hydrolysis step is essentially performed as described above for embodiment a, using the same casein-specific proteinases. Any adaptations required, depending on the starting preparation used, will be evident to those skilled in the art, also drawing on the present description.
The degree of hydrolysis will preferably be such that after completion of the hydrolysis step, more than 90%, more preferably to more than 99%, and most preferably essentially all casein present in the starting preparation has been cleaved into smaller fragments. The level of still intact casein molecules after the hydrolysis step is preferably less than 0.1 wt % or more preferably less than 0.01 wt %.
The hydrolysis is preferably carried out to such a degree that the level of antigenic casein hydrolysis fragments (including any uncleaved/intact casein) is less than 1 wt %, preferably less than 0.1 wt %.
According to a particular embodiment, the protein preparation obtained after hydrolysis and containing the casein hydrolysis fragments, is already free from casein epitopes, which means that the casein and/or the (antigenic) fragments thereof have been cleaved to such a degree that casein epitopes can no longer be detected in suitable immunological assays, such as ELISA, using casein-specific antibodies.
However, as a rule, such extensive hydrolysis is not required to obtain a protein preparation free from casein epitopes, since any small antigenic casein hydrolysis fragments still present can likewise be removed in the course of a subsequent separation step, as described below.
It will also be clear to those skilled in the art that this embodiment can be used not only to remove/separate off intact casein molecules but also to remove/separate off casein fragments, in particular antigenic casein fragments.
To separate off the casein fragments obtained by hydrolysis, any suitable separation method can be used, a separation method on the basis of molecular mass and/or molecular size again being preferred. In particular, ultrafiltration or a similar technique can be used, the desired fraction not being the permeate (as in embodiment a. above) but the retentate which will contain the one or more desired protein constituents.
In ultrafiltration, a membrane having a suitable molecular cut-off value is used. Dependent upon said cut-off value, solely the casein hydrolysis fragments can be separated off, orxe2x80x94by using a suitably higher cut-off valuexe2x80x94simultaneously one or more of the small(er) further protein constituents, which have remained intact, can also be removed.
The removal of essentially only the casein hydrolysis fragments will generally involve the use of a membrane having a molecular cut-off value of 10 kDa or less, depending on the degree of hydrolysis.
The degree of hydrolysis and the molecular cut-off value of the ultrafiltration membrane used are preferably chosen such that the level of (antigenic) casein hydrolysis fragments and/or casein epitopes in the retentate obtained after ultrafiltration is less than 0.1 wt %, preferably less than 0.01 wt%.
Most preferably, the degree of hydrolysis and the molecular cut-off value are chosen such that all antigenic casein hydrolysis fragments and/or casein epitopes can be separated off, so that it is no longer possible to detect, by means of suitable immunological assays using casein-specific antibodies, such as ELISA, any epitopes of casein in the protein preparation obtained after ultrafiltration. Such a preparation is here referred to as xe2x80x9cfree from casein epitopesxe2x80x9d.
If the starting material is milk, whey or a solution of milk proteins or whey proteins, what is obtained after the casein hydrolysis fragments have been separated off will generally be a mixture of proteins. This mixture may be further separated according to methods known per se, to obtain the separate protein constituents in purified or essentially pure form. This can be done, for example, by precipitation, chromatographic techniques, or by further separation on the basis of molecular mass or molecular size. It is thus possible, by successive ultrafiltration steps with increasing molecular cut-off values of the membrane, to achieve fractionation of the milk proteins.
This embodiment of the invention can be used, in particular, to obtain milk protein preparations, in particular preparations comprising one or more whey proteins such as xcex1-Lac, xcex2-Lg, BSA and IgG. However, this embodiment can also be used for purifying or isolating proteins not native to natural milk, starting from a casein-containing medium. All these protein preparations are preferably free from casein epitopes, as defined above.
The (whey) protein preparations thus obtained, in particular the preparations free from casein epitopes, can be used for preparing food preparations such as infant formula, for preventing immunological reactions against casein, in particular xcex2-casein.
With respect to the invention it is further noted that it differs from the action of bacterial proteinases during the maturation of cheesexe2x80x94which is outside the scope of the inventionxe2x80x94in that the casein/caseinate, and preferably also the further protein constituents, during the hydrolysis are in solution, which may or may not be concentrated and will generally be aqueous; in cheese-making, the casein-cleaving enzymes act on the precipitated casein in the curd.
Moreover, the cleavage of casein in the cheese milk takes place under the influence of a specific enzyme (a curdling enzyme such as chymosin). The action, and particularly the specificity, of the proteinases used according to the invention differ demonstrably, however, from that of such curdling enzymes. Thus, according to one aspect of the invention, the specific action of chymosin on casein, in particular with respect to the cleavage of the phenylalanine/methionine bond, is disclaimed, even though the invention in the widest sense is not limited to a specific type of enzymatic reaction.
Although the invention has been described above with respect to two different embodiments, it should be understood that these embodiments can also be combined in that, after the specific hydrolysis of the casein/caseinate-containing (milk) protein preparation, both the casein hydrolysis fragments and the proteins which have remained intact are obtained as two separate fractions by means of a suitable separation technique as described above. These fractions can then be further processed and/or used in the above-described manner. Other adaptations and uses of the teachings of the invention, which are within the scope of the following claims, will be obvious to those skilled in the art.